The present invention concerns flow velocity measurement and display techniques, and in particular the measurement of blood flow in blood vessels, veins or arteries, using methods non-invasive to the patient.
In many cases, certain parameters, need to be considered when assessing flow velocities, so that, in an application to the medical field, a precise diagnosis can be given of the instantaneous and local condition of a segment of blood vessel.
Two types of equipment are already known which have tried to solve the aforesaid problems, each one collecting information by measuring means and supplying processable electrical signals which are applied to a display equipment of a known type, through the technical means currently used to produce images on a screen.
These two types of already known equipment differ by the design of the measuring element which in one case, is a continuous-transmission Doppler velocimeter, and in the second case, a pulsed-transmission Doppler velocimeter.
In the technique using the continuous-transmission Doppler velocimeter, the emitting transducer emits a continuous ultrasonic beam pointed in the direction of the area to be scanned, to produce a reflected beam which is picked up by a transmit-receive transducer.
The scanning field of the transmitted beam can in a way be monitored as a measuring band and enables the mean value of the different flow velocities encountered along said measuring line to be obtained.
When a measurement has been taken in a given position, then the scanning field should be shifted by lateral translation of the transmitted beam, in order to proceed with scanning and measuring of a second juxtaposed segment of vessel.
The shifting from one measuring band to another can be done mechanically, thus permitting use of a focussed transducer, providing, a good transverse resolution. However, it is conceivable that such a system cannot validly be used when the object is to obtain a real-time display, namely a display permitting a monitoring of any instantaneous alteration. Indeed, the mechanical shifting of the transmitter makes it impossible to obtain, within a short period of time, a sufficient number of transverse measurements permitting a real-time display.
It is possible to resort to a different system, using an electronic shift. To this effect, the transmitter is composed of a large number of small-size transducers, in alignment, which can be successively switched over to the transmitting generator, each one thus delivering a separate ultrasonic beam pointed in the direction of the area to be scanned. This type of apparatus eliminates any subjection inherent in the mechanical shift, but it also has a considerable number of disadvantages. Indeed, because of the small size of the transducers, there is scattering of each transmitted beam, hence, a poor lateral resolution. This disadvantage does not permit measurements over a great number of parallel, close-together bands, so that the object, which is to obtain a real-time display of the scanned area, is not achieved.
The second technique consists in using, as measuring apparatus, a pulse-transmission Doppler velocimeter. As in the preceding example, a beam is transmitted to define a measuring line. Said pulsed ultrasonic beam enables measurement of the velocity along several successive points on the measuring line. It becomes then possible to obtain, not really a measurement of the mean velocity, as with the continuous-transmission velocimeter, but a measurement which corresponds to successive points on one line and therefore, a point-by-point transverse assessment of the flowing velocity inside part of a segment of vessel.
With such a technique, it should nonetheless be proceeded as indicated hereinabove to obtain several successive measuring lines. As in the preceding case, the shifting from one measuring line to another can be effected mechanically or, preferably electronically, but with the same disadvantages as those already indicated.
Such technique therefore does not permit real-time simultaneous information for a large number of lines to be obtained nor an instantaneous display of a large area of a segment of vessel.
Another disadvantage with this technique resides in the fact that it is not possible to use a pulse repetition rate permitting to reach without ambiguity, relatively important scanning depths, greater in any case than 1 or 2 cm, in the Doppler frequency ranges normally encountered.
Such a limitation is a real drawback in the technical field concerned here.
It is the object of the present invention to solve the afore-mentioned problem and to propose a new method and new equipment permitting to obtain the real-time measurement and display of flow velocities in segments of vessel.
And it is a particular object of the invention to obtain such results but with those devices, receiving or utilizing supplied electronic information, conventionally used to display information of any type of display screen.
The object of the invention is more particularly to propose a method and apparatus which can be used in the medical field for reading information relative to parameters of blood circulation in blood-vessels, veins or arteries, without resorting to invasive devices.
A further object of the invention is to propose a new method and new equipment which are also adapted to supply, in addition, electrical information capable of simultaneously feeding echography apparatus.